Systems and methods for particle size determination and control in a fluidized bed reactor

ABSTRACT

Systems and methods are provided for determining the size of particles within a fluidized bed reactor. The pressure of gas adjacent a gas inlet and adjacent a gas outlet of the reactor are measured with pressure sensors. An algorithm is applied to at least one of the pressure measurements to determine the size of particles within the reactor. The determined size of the particles can be used to control the operation of the reactor. A dosing system and method is provided for measuring defined volumes of particles for transport to the reactor.

BACKGROUND

Polycrystalline silicon is a raw material used to produce manycommercial products including, for example, integrated circuits andphotovoltaic (i.e., solar) cells. Polycrystalline silicon is typicallyproduced by a chemical vapor deposition mechanism in which silicon isdeposited from a thermally decomposable silicon compound onto siliconseed particles in a fluidized bed reactor. These seed particlescontinuously grow in size until they exit the reactor as polycrystallinesilicon particles product (i.e., “granular” polycrystalline silicon).Suitable decomposable silicon compounds include, for example, silane andhalosilanes (e.g., trichlorosilane).

Polycrystalline seed particles may be added to the reaction chamber toinitiate deposition of silicon. A variety of reactions may take place inthe reaction chamber. Silicon deposits from silane onto a siliconparticle, resulting in the particle growing in size. As the reactionprogresses, silicon particles grow to a desired size and are removedfrom the reaction chamber and new seed particles are added to thereaction chamber.

Other processes conducted in fluidized bed reactors result in thereduction in size of particles within the reactors. For example,metallurgical-grade silicon and hydrochloric acid may be burned withinthe reaction chamber to produce trichlorosilane. During this process,the metallurgical-grade silicon particles are eroded and decrease insize as the reaction progresses. These particles are eventually removedonce the particles have decreased to a certain size.

Various methods have been used to attempt to estimate the size ofparticles in the reaction chamber. In one method, the sample particlesare removed from the reactor and allowed to cool, after which they aremeasured. But this method is incapable of real-time measurement of theparticle size because there is considerable delay between removal of theparticle from the reactor and determination of its size. Another methodestimates the size of particles via stoichiometric methods. Still othermethods attempt to estimate particle size based on the pressure of gaswithin the reaction chamber of the fluidized bed reactor. These methodshave generally yielded unsatisfactory results.

This Background section is intended to introduce the reader to variousaspects of art that may be related to various aspects of the presentdisclosure, which are described and/or claimed below. This discussion isbelieved to be helpful in providing the reader with backgroundinformation to facilitate a better understanding of the various aspectsof the present disclosure. Accordingly, it should be understood thatthese statements are to be read in this light, and not as admissions ofprior art.

BRIEF SUMMARY

One aspect is a system for determining a size of particles in afluidized bed reactor. The system comprises a fluidized bed reactor, apressure sensor, and a processor. The fluidized bed reactor contains aplurality of particles and has an inlet and an outlet. The pressuresensor is positioned adjacent the reactor and is configured to measure agas pressure in at least one of the inlet and the outlet of the reactor.The processor is in communication with the pressure sensor and isconfigured to determine the size of at least one of the plurality ofparticles in the reactor by use of an algorithm and the measured gaspressure.

Another aspect is a system for determining a diameter of at least one ofa plurality of particles in a fluidized bed reactor. The systemcomprises an inlet pressure sensor and a processor. The inlet pressuresensor is positioned adjacent a gas inlet of the fluidized bed reactorand is configured to measure a gas pressure in the gas inlet of thereactor. The processor is in communication with the first pressuresensor and is configured to determine the diameter of at least one ofthe plurality of particles in the reactor by applying a first algorithmto the measured gas pressure.

Still another aspect is a method for determining a size of at least oneof plurality of particles in a fluidized bed reactor. The methodcomprises measuring a gas pressure in an inlet of the reactor with aninlet pressure sensor. The measured gas pressure in the inlet of thereactor is then communicated to a processor. The processor thendetermines the size of at least one of the plurality of particles in thefluidized bed reactor based at least in part on an algorithm applied tothe gas pressure in the inlet of the reactor measured by the inletpressure sensor.

Various refinements exist of the features noted in relation to theabove-mentioned aspects. Further features may also be incorporated inthe above-mentioned aspects as well. These refinements and additionalfeatures may exist individually or in any combination. For instance,various features discussed below in relation to any of the illustratedembodiments may be incorporated into any of the above-described aspects,alone or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are not to scale and certain features may be exaggeratedfor ease of illustration.

FIG. 1 is a schematic of an exemplary fluidized bed reactor;

FIG. 2 is a schematic of an exemplary volumetric metering system for usewith the fluidized bed reactor of FIG. 1;

FIG. 3 is a flow diagram showing a method of determining a size of aparticle in a fluidized bed reactor;

FIG. 4 is a flow diagram showing a method of measuring and dispensing avolume of particles from a dosing drum into the fluidized bed reactor;and

FIG. 5 is a chart showing a comparison of estimated mean particle sizeaccording to the method of FIG. 3.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The systems and methods described herein enable accurate real-timedetermination of the size of particles within fluidized bed reactorsbased on the pressure of gas adjacent the gas inlet and/or outlet of thereactor. Previous attempts to estimate the size of particles in thechamber were based on pressure measurements obtained by sensors withinthe reaction chamber of the reactor. However, such measurements wereinaccurate. For example, the pressure sensors often yielded inaccuratereadings because the sensors were subject to contact with the particles.This contact was determined to result in fouling of the sensors.Moreover, this contact also resulted in the pressure sensorscontaminating the particles as the particles abraded the exposedportions of the pressure sensors.

Referring initially to FIG. 1, an exemplary fluidized bed reactor isindicated generally at 100. The reactor 100 includes a reaction chamber102 for receiving a plurality of particles 101. The reaction chamber 102is defined by a shell 104 having an inner surface 106 and an outersurface 108. The shell 104 may be lined with a liner (not shown)positioned adjacent the inner surface 106 thereof and constructed from asuitably non-reactive material (e.g., quartz or graphite). The shell 104has a lower end 110 and an opposite upper end 112 connected together byspaced-apart sidewalls 114. In the exemplary embodiment, the shell 104is cylindrically shaped, although in other embodiments the shell isshaped differently.

The shell 104 has a gas inlet 118 for introducing gas into the reactionchamber 102 and a gas outlet 116 for the removal of gas from thereaction chamber. In the exemplary embodiment, the gases introduced andremoved from the reaction chamber 102 may be of any suitable type usedin the production of silicon-containing products. For example, the gasmay be a thermally decomposable silicon-containing gas or any of thesilanes (e.g., monosilane, trichlorosilane, dichlorosilane, ortribromosilane) when the fluidized bed reactor is used to generategranular polysilicon.

The shell 104 also has a particle inlet 120 for the introduction ofparticles into the reaction chamber 102. A particle outlet 122 in theshell 104 facilitates removal of particles from the reaction chamber102. In the exemplary embodiment, the particles introduced and removedfrom the reaction chamber 102 may be of any suitable type used in theproduction of silicon-containing products. For example, the particlesmay be granular polysilicon.

As shown in FIG. 1, the gas inlet 118 and the particle outlet 122 arepositioned adjacent the lower end 110 of the shell 104, while the gasoutlet 116 and particle inlet 120 are positioned adjacent the upper end112 of the shell. The positions of these components in relation to theshell 104 are exemplary in nature, and may be changed without departingfrom the scope of the embodiments.

A plate 124 (i.e., a distributor) is positioned within the shell 104near the lower end 110 of the shell. The plate 124 may be spaced fromthe lower end 110 of the shell 104 by any suitable distance. The plate124 is generally porous and has openings formed therein that are sizedto permit the passage of gas therethrough while preventing particlesfrom passing through the openings. The plate 124 is constructed from anysuitably non-reactive material (e.g., quartz, graphite, or siliconcarbide).

The fluidized bed reactor 100 may also include a heat source (not shown)for heating the reaction chamber 102 and the gases and particlescontained therein. In the exemplary embodiment, the heat source is anelectrical resistance heater positioned adjacent the outer surface 108of the shell 104.

A first pressure sensor 126 (i.e., an “inlet pressure sensor”) ispositioned in the shell 104 in a plenum 132 adjacent the gas inlet 118or in the gas inlet adjacent the plenum. A second pressure sensor 128(i.e., an “outlet pressure sensor”) is positioned in the gas outlet 116.The first pressure sensor 126 is configured to measure the pressure(e.g., pressure amplitude fluctuations or absolute pressure) of gas inthe plenum 132 adjacent the gas inlet 118. The pressure of gas in theplenum 132 may be representative of the gas pressure below the plate124. The second pressure sensor 128 is configured to measure thepressure (e.g., pressure amplitude fluctuations or absolute pressure) ofgas in the gas outlet 116. The pressure of gas in the gas outlet 116 maybe representative of gas pressure in the reaction chamber 102. Becauseof their positions, the pressure sensors 126, 128 do not contact theparticles 101 disposed within the reaction chamber 102. Accordingly, thepressure sensors 126, 128 do not contaminate these particles 101.

The pressure sensors 126, 128 are connected to a processor 130 by anysuitable communication mechanism (e.g., wired and/or wirelesscommunication mechanisms). The processor 130 is a suitable computingdevice which is operable to perform calculations based at least in parton the pressures measured by the pressure sensors 126, 128 andcommunicated to the processor. The processor 130 may include varioustypes of computer-readable media, input/output devices, and othercomponents used in computing devices.

A dosing system of embodiment is shown in FIG. 2 and indicated generallyat 200. The dosing system 200 is used to meter (i.e., dose) definedvolumes of particles 101 for transport into the reaction chamber 102 ofthe fluidized bed reactor 100 through the particle inlet 120.

The dosing system 200 includes a dosing drum 202 having an upper end 204and a lower end 206. An inlet valve 208 (i.e., a “first valve”) ispositioned adjacent the upper end 204 for controlling the flow ofparticles 101 into the dosing drum 202 from a seed hopper 210. The seedhopper 210 is a container configured for storing bulk volumes ofparticles 101. An outlet valve 212 (i.e., a “second valve”) ispositioned adjacent the lower end 206 of the dosing drum 202 andcontrols the flow of particles 101 from the dosing drum into theparticle inlet 120 of the fluidized bed reactor 100.

The valves 208, 212 are any suitable valves that are operable to controlthe flow of the particles without contaminating the particles. Thevalves 208, 212 are actuated by respective valve actuators 214, 216which are in turn controlled by and communicatively coupled to a valveprocessor (not shown) and/or the processor 130 described above inrelation to FIG. 1.

An upper limit sensor 218 is positioned adjacent the upper end 204 ofthe dosing drum 202 and a lower limit sensor 220 is positioned adjacentthe lower end 206 of the dosing drum. In the exemplary embodiment, thelimit sensors 218, 220 are nuclear level switches and each includerespective emitters 222, 226 and receivers 224, 228. The emitters 222,226 and receivers 224, 228 are operable to determine when particles aredisposed therebetween. The emitters 222, 226 emit radiation therefrom ina linear path and the emitters 224, 228 receive this radiation. Whenobjects (i.e., particles) obstruct the linear path, radiation emittedfrom the emitters 222, 226 is blocked by the objects which reduces theintensity of radiation received by the receivers 224, 228. The limitsensors 218, 220 are thus capable of indicating when particles aredisposed at or above respective levels within the dosing drum 202.

Accordingly, the upper limit sensor 218 is operable to determine whenthe dosing drum 202 is filled with particles at a level greater than orequal to a first level 230. The lower limit sensor 220 is operable todetermine when the dosing drum 202 is filled with particles less than asecond level 232.

FIG. 3 shows a method 300 for determining a size of particles in thefluidized bed reactor 100. The method 300 begins in block 310 withmeasuring the pressure of gas in the gas inlet 118 of the reactionchamber 102 using the first pressure sensor 126. This measured gaspressure is then communicated to the processor 130 in block 320.

The processor 130 then determines the size of the particles in block330. To make this determination, the processor 130 applies an algorithmor formula to the measured gas pressure. The algorithm or formula usedin the exemplary embodiment is reproduced below.

$\frac{d_{s_{i}}}{d_{s_{k}}} = \left\lbrack {\frac{\mu_{i}}{\mu_{k}} \cdot \left( {\frac{U_{i}}{U_{{mf}_{k}}} + {\frac{\sigma_{p_{i}} \cdot M_{k}}{\sigma_{p_{k}} \cdot M_{i}} \cdot \left( {1 - \frac{U_{j}}{U_{{mf}_{k}}}} \right)}} \right)} \right\rbrack^{1/2}$

Subscript i represents the value of a variable at a time t=t_(i) andsubscript k represents the value of a variable at a t=t_(k). A time oft_(i) is an initial time, while a time of t_(k) is a later point intime. The variables in the above equation represent: d_(s)=sauter meandiameter of particles, μ=the viscosity of gas, U=gas superficialvelocity, U_(mf)=minimum fluidization velocity, σ_(ρ)=amplitude ofpressure fluctuations, and M=mass of particles in the reaction chamber.Load cells or other similar mechanisms (not shown) may be used todetermine the mass of the particles in the reaction chamber. Given thetype of gas, its temperature and pressure, the viscosity of the gas isreadily determined based on the kinetic theory of gases. Moreover, otherembodiments may use different algorithms to determine size of particlesbased on the measured pressure. These algorithms may rely in part on thegas pressure measured by both the first pressure sensor 126 and secondpressure sensor 128.

Use of the algorithm thus results in the determination of the size(e.g., sauter mean diameter or diameter) of particles in the reactionchamber 120. The determined size may be an average of the size of allthe particles in the reaction chamber. This average size may be surfaceaveraged, size averaged, or volume averaged.

In some embodiments, method 300 is used as a feedback control for theoperation of the fluidized bed reactor 100. As such, the processperformed by the fluidized bed reactor 100 may be altered based on thedetermined size of the particles. For example, if the method 300determines the particle diameter is above a threshold level, particlesmay be removed from the reaction chamber 102 and new particles may beadded to the reaction chamber. The rate of removal and/or addition ofparticles may be increased or decreased as well. In some embodiments,the size of particles added to the reaction chamber 102 may be increasedor decreased.

In another instance, if the method 300 determines the particle diameteris below a threshold level, the flow rate of the gas is decreased inorder to reduce the rate of particle growth. The flow rate of gas mayinstead be increased, if necessary, to avoid de-fluidization of theparticles within the reaction chamber 102.

In another example, if the method 300 determines the particle diameteris below a threshold level, particles may be removed from the reactionchamber 102 and new particles may be added to the reaction chamber.

In another embodiment, the size of particles within the reaction chamber102 may be used to measure the performance of the fluidized bed reactor100 (e.g., rates of conversion/consumption of the decomposing gas anddust production). For example, if the rate of conversion/consumption ofthe decomposing gas in the reaction chamber 102 decreases, the size ofparticles within the reaction chamber increase as well. This change inthe particle size can be monitored according to the method 300. Tocompensate for the decrease in the conversion/consumption of thedecomposing gas, lower quantities of larger sized particles or largerquantities of smaller sized particles may be added to the reactionchamber 102.

In another instance, an increase in the size of particles within thereaction chamber 102 can indicate a corresponding increase in the rateof dust production. To decrease the rate of dust production, the flowrate of the gas may be altered and/or the size and/or quantity ofparticles added to the reaction chamber may be changed.

Moreover, in other embodiments the pressure is not measured in the gasinlet 118 and the pressure is measured instead with the second pressuresensor 128 in block 310. The measured pressure in the outlet 116 is thenused in the subsequent steps of the method 300. In another embodiment, adifferential pressure measured between the gas inlet 118 and the gasoutlet 116 is used in block 310. The measured differential pressure isthen used in the subsequent steps of the method 300.

The method 300 can continue to be performed at regular intervals inorder to determine the size of particles within the reaction chamber102. For example, method 300 can be performed multiple times per secondor method 300 or at any other suitable frequency (e.g., multiple timesper minute or hour).

FIG. 5 shows a comparison of estimated mean particle size according tothe method 300 with actual physical measurement of particle size.

FIG. 4 depicts a method 400 of measuring a defined volume of particleswith the dosing system 200 of FIG. 2. The defined volume is equal to avolume of the dosing drum 202 between a first level 230 and a secondlevel 232. As described above, the upper limit sensor 218 is positionedto detect when the dosing drum 202 is filled with particles at or abovethe first level 230. The lower limit sensor 220 is positioned to detectwhen the dosing drum 202 is filled with particles at or below the secondlevel 232. As the dimensions of the dosing drum 202 and the distancebetween the first level 230 and the second level 232 are known, thevolume of the defined volume is readily determinable.

The outlet valve 212 is closed. Method 400 begins in block 410 withopening the inlet valve 208 such that particles flow from the seedhopper 210, through the inlet valve and into the dosing drum 202.

The flow of particles into the dosing drum 202 continues in block 420until the level of particles reaches the first level 230. The system 200uses the upper limit sensor 218 to determine when the particles reachthe first level 230. Once the level of particles in the dosing drum 202reaches the first level 230, the inlet valve 208 is closed in block 430and the flow of particles into the dosing drum 202 is stopped.

The outlet valve 212 is then opened in block 440 and the defined volumeof particles is transported from the dosing drum 202 into the particleinlet 120 of the reaction chamber 102. The dosing drum 202 may bepositioned with respect to the particle inlet 120 such that particlesare transported to the particle inlet as by gravity or other suitablemethods (e.g., pneumatic transport using a pressurized inert gas).

The outlet valve 212 is closed in block 450 when the lower limit sensor220 determines that the particles are at the second level 232 within thedosing drum 202.

The steps of the method 400 may then be repeated as necessary totransport defined volumes of particles to the particle inlet 120 of thereaction chamber 102. The steps of the method 400 thus provide for theaccurate, non-invasive measurement of defined volumes of particles.

While the systems and methods described above are directed to fluidizedbed reactors for use with thermally decomposable gases, they may also beused in other processes conducted in fluidized bed reactors. Examples ofthese other processes include: fluid catalytic cracking (where thecatalyst particle changes with time), partial oxidation of n-butane tomaleic anhydride, combustion of coal, wood, or shale, calcination ofalumina, roasting of sulfide ores (e.g., ZnS, Cu2S, etc.), anddesulfurization of flue gases. Such processes use different types ofparticles than those described above.

The order of execution or performance of the operations in embodimentsof the invention illustrated and described herein is not essential,unless otherwise specified. That is, the operations may be performed inany order, unless otherwise specified, and embodiments of the inventionmay include additional or fewer operations than those disclosed herein.For example, it is contemplated that executing or performing aparticular operation before, contemporaneously with, or after anotheroperation is within the scope of aspects of the invention.

When introducing elements of the present invention or the embodiment(s)thereof, the articles “a”, “an”, “the” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising”,“including” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description and shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

1. A system for determining a size of particles in a fluidized bedreactor, the system comprising: a fluidized bed reactor containing aplurality of particles and having an inlet and an outlet; a pressuresensor positioned adjacent the reactor, the pressure sensor configuredto measure a gas pressure in at least one of the inlet and the outlet ofthe reactor; and a processor in communication with the pressure sensor,the processor configured to determine the size of at least one of theplurality of particles in the reactor by use of an algorithm and themeasured gas pressure.
 2. The system of claim 1 wherein the inletpressure sensor is positioned adjacent the gas inlet.
 3. The system ofclaim 2 wherein the gas inlet is adjacent a plenum.
 4. The system ofclaim 1 wherein the outlet pressure sensor is positioned adjacent thegas outlet.
 5. The system of claim 1 wherein the reactor has a shell andan additional pressure sensor is positioned adjacent the shell.
 6. Thesystem of claim 1 wherein the processor is configured to determine adiameter of at least one of the plurality of particles by applying thealgorithm to the gas pressure in the reactor measured by the pressuresensor.
 7. The system of claim 6 wherein the processor is configured todetermine a surface averaged diameter of at least one of the pluralityof particles by applying the algorithm to the gas pressure in thereactor measured by the pressure sensor.
 8. A system for determining adiameter of at least one of a plurality of particles in a fluidized bedreactor, the system comprising: an inlet pressure sensor positionedadjacent a gas inlet of the fluidized bed reactor, the inlet pressuresensor configured to measure a gas pressure in the gas inlet of thereactor; a processor in communication with the inlet pressure sensor,the processor configured to determine the diameter of at least one ofthe plurality of particles in the reactor by applying a first algorithmto the measured gas pressure.
 9. The system of claim 8 furthercomprising an outlet pressure sensor positioned adjacent a gas outlet ofthe fluidized bed reactor.
 10. The system of claim 9 wherein theprocessor is in communication with the outlet pressure sensor and theprocessor is configured to determine the diameter of at least one of theplurality of particles in the reactor by applying the algorithm to thegas pressure measured by the inlet pressure sensor and the gas pressuremeasured by the outlet pressure sensor.
 11. A method for determining asize of at least one of plurality of particles in a fluidized bedreactor, the method comprising: measuring a gas pressure in an inlet ofthe reactor with an inlet pressure sensor; communicating the measuredgas pressure in the inlet of the reactor to a processor; anddetermining, using the processor, the size of at least one of theplurality of particles in the fluidized bed reactor based at least inpart on an algorithm applied to the gas pressure in the inlet of thereactor measured by the inlet pressure sensor.
 12. The method of claim11 wherein determining, using the processor, the size of at least one ofthe plurality of particles in the fluidized bed reactor includesdetermining, using the processor, a diameter of at least one of theplurality of particles in the fluidized bed reactor.
 13. The method ofclaim 11 further comprising measuring a gas pressure in an outlet of thereactor with an outlet pressure sensor.
 14. The method of claim 13further wherein determining, using the processor, the size of at leastone of the plurality of particles in the fluidized bed reactor includesapplying the algorithm to the gas pressure measured by the inletpressure sensor and the gas pressure measured by the outlet pressuresensor.
 15. The method of claim 14 wherein determining, with theprocessor, the size of at least one of the plurality of particles in thefluidized bed reactor includes determining, using the processor, adiameter of at least one of the plurality of particles in the fluidizedbed reactor.
 16. The method of claim 11 further comprising controllingthe operation of the fluidized bed reactor based at least in part on thedetermined size of at least one of the plurality of particles in thefluidized bed reactor.
 17. The method of claim 16 wherein controllingoperation of the fluidized bed reactor includes one of increasing therate of addition of particles to the fluidized bed reactor andincreasing the rate of removal of particles from the fluidized bedreactor.
 18. The method of claim 16 wherein controlling operation of thefluidized bed reactor includes one of decreasing the rate of addition ofparticles to the fluidized bed reactor and decreasing the rate ofremoval of particles from the fluidized bed reactor.
 19. The method ofclaim 16 wherein controlling operation of the fluidized bed reactorincludes increasing the flow rate of gas within the fluidized bedreactor when the determined size of at least one of the plurality ofparticles exceeds a threshold level.
 20. The method of claim 16 whereincontrolling operation of the fluidized bed reactor includes decreasingthe flow rate of gas within the fluidized bed reactor when thedetermined size of at least one of the plurality of particles exceeds athreshold level.
 21. The method of claim 11 further comprisingdetermining, with the processor, the rate at which the gas is consumedbased on the determined size of at least one of the particles.
 22. Asystem for measuring a volume of particles for placement within afluidized bed reactor for use with thermally decomposablesilicon-containing gas, the system comprising: a dosing drum forreceiving particles from a source; an upper limit sensor positionedrelative to the dosing drum to detect when the volume of particles inthe dosing drum is at a first level; and a lower limit sensor positionedrelative to the dosing drum to detect when the volume of particles inthe dosing drum is at a second level, the second level being less thanthe first level.
 23. The system of claim 22 wherein the upper limitsensor comprises an emitter and a receptor.
 24. The system of claim 23wherein the emitter and the receptor are positioned relative to thedosing drum such that when the volume of particles is equal to orgreater than the first level, at least one of the particles blocks alinear path between the emitter and the receptor.
 25. The system ofclaim 22 wherein the lower limit sensor comprises an emitter and areceptor.
 26. The system of claim 25 wherein the emitter and thereceptor are positioned relative to the dosing drum such that when thevolume of particles is less than the second level a linear path betweenthe emitter and the receptor is unobstructed by the particles.
 27. Thesystem of claim 22 further comprising a first valve for controlling theflow of particles from the source into the dosing drum.
 28. The systemof claim 22 further comprising a second valve for controlling the flowof particles from the dosing drum into a receptacle.
 29. The system ofclaim 28 wherein the receptacle is a fluidized bed reactor.